1. Field of the Invention
This invention relates to transition metal bis(dithiolene) complex polymers and copolymers, and their preparation by polymerization of bifunctionalized transition metal bis(dithiolene) complexes.
2. Description of Related Art
Over the past 30 years, there has been a considerable effort devoted to the synthesis and understanding of transition metal bis(dithiolenes).sup.1 and structurally related complexes.sup.2 which possess interesting electrochemical, optical, magnetic, liquid crystalline,.sup.3 electrically conductive, superconductive.sup.4, and near-infrared ("NIR") absorption properties..sup.5-7
A number of electroactive and conductive polymers and oligomers based on the square planar MS.sub.4 center have also been prepared. These include poly(metal tetrathiooxalates),.sup.8 poly(metal ethylenetetrathiolates),.sup.9 poly(metal tetrathiosquarates),.sup.10 poly(metal tetrathiafulvalenetetrathiolates),.sup.11, 12 poly(metal tetrathianaphthalenes),.sup.13 and poly(metal benzenetetrathiolates)..sup.14
Although many of these polymers are potentially useful because of their electroactive and conductive properties, most of them are insoluble and infusible solids due to their ribbonlike rigid structure. During synthesis some of these systems possess solubility that may be attributed to the high charge density along the polymer backbone, but precipitation to insoluble and infusible powders prohibits processing of the polymer for practical application.
In order to address the low solubility of these fully conjugated polymers, the inventors herein have discovered the possibility of incorporating square planar metal complexes [i.e. metal bis(dithiolenes)] into the main chain of polymers that contain flexible units. The inventors previously reported.sup.15-18 on the synthesis of a novel metal complex polymer, poly[[1,1'-oxybis[4-(1,2-dithiolatoethenyl)benzene]] nickel(II)], having the following structure: ##STR1## where X is oxygen.
Although this polymer, in its reduced form, is generally soluble in a variety of both aqueous and organic solvents, and exhibits electrochemical properties analogous to transition metal bis(dithiolenes), it tends to be generally insoluble in its oxidized and neutral forms. Thus, its potential application is limited. In addition, low molecular weights were obtained due to intrinsic problems of the metal complexation polymerization technique used.
It can be hypothesized that solubility and processability of compound (I) could be improved by introducing a flexible linkage X into the main chain. The synthesis of this polymer, as previously reported by the inventors, involved complexation of a tetrathiolate ligand precursor prepared via a bis(dithiocarbonate) (shown below), with a stoichiometric amount of Ni.sup.2+. ##STR2##
This type of synthesis tends to become problematical as the flexible linkage X becomes longer, due to the difficulty in preparing the precursor (2). For example, when the linkage is docosane, the synthesis of the ligand generally requires multiple steps and therefore the overall yield tends to be low. As a general rule in organic chemistry, increasing the substrate size and flexible side chain length significantly reduces the reactivity of the functional group in the compound due to steric blocking of the active site. From a kinetic viewpoint, the number of effective collisions between molecules may also be reduced. Typically, long reaction times, severe reaction conditions and low yields are encountered in reactions involving large molecules. Long flexible chains along the polymer backbone are generally needed in order to further increase the solubility of the polymers. However, this tends to further increase synthetic difficulties, as well as lead to added expense, lower yields, and increased time constraints. Time consuming, highly involved multistep syntheses may be required to produce products that possess little synthetic versatility. Another problem associated with such a synthesis is in maintaining stoichiometric balance between the two reactants.
Thus, there is a need to develop improved classes of polymers based on square planar MS.sub.4 centers, and improved syntheses of such polymers. It is an object of this invention to provide such polymers and syntheses which address at least some of the shortcomings of the prior art.